1. Field of the Invention
The present invention relates to a liquid crystal display, and more particularly, to a liquid crystal display panel and method for fabricating the same by a liquid crystal dropping method.
2. Discussion of the Related Art
A thin flat panel display tends to have a thickness of no more than a few centimeters. Particularly, a liquid crystal display (LCD) has a wide scope of applications, such as notebook computers, computer monitors, gauge monitors for space crafts, and air crafts, and the like.
Referring to FIG. 1, an LCD is provided with a lower substrate 1 having a plurality of thin film transistors and pixel electrodes formed thereon, an upper substrate 3 facing into the lower substrate 1 having a black matrix (BM), a color filter layer, and a common electrode, and a liquid crystal layer 5 between the two substrates 1 and 3. A sealant 7 is formed between the lower and upper substrates 1 and 3, to bond the substrates and prevent the liquid crystal from leaking.
In the foregoing LCD, a vacuum injection method has been used for forming the liquid crystal layer between the lower substrate 1 and the upper substrate 3. In such a method, after the lower substrate 1 and the upper substrate 3 are bonded together, a liquid crystal is injected between the two substrates by using capillary phenomenon and a pressure difference. However, the vacuum injection method takes much time to fill the liquid crystal between the substrates. As a result, productivity is much reduced as the substrate becomes large. Consequently, a method called a liquid crystal dropping method is suggested for solving such a problem. A method for fabricating an LCD panel by using a related art liquid crystal dropping method will be explained with reference to the attached drawings.
FIGS. 2A to 2D illustrate perspective views showing a method for fabricating an LCD panel by using a related art liquid crystal dropping method. For convenience, only one unit cell is illustrated in the drawings.
Referring to FIG. 2A, a lower substrate 1 and an upper substrate 3 are prepared for the process. A plurality of gate lines and data lines (both not shown) are formed on the lower substrate 1 to cross each other defining pixel regions. A thin film transistor is formed at every crossing point of the gate lines and the data lines. A pixel electrode is formed at every pixel regions connected to the thin film transistor.
A black matrix is formed on the upper substrate 3 for shielding a light leakage from the gate lines, the data lines, and the thin film transistors regions. A color filter layer of red, green, and blue is formed thereon. A common electrode is formed thereon in this order. An alignment film is formed on both of the lower substrate 1 and the upper substrate 3 for an initial orientation of the liquid crystal.
Referring to FIG. 2B, a sealant 7 is coated on the lower substrate 1, and a liquid crystal 5 is dropped thereon to form a liquid crystal layer. Then, spacers (not shown) are spread on the upper substrate 3 for maintaining a cell gap. The spacers may be ball spacers spread on the substrate, or column spacers attached to the substrate.
In the liquid crystal dropping method, the liquid crystal layer is placed between the attached substrates before hardening a sealant. Accordingly, if a thermo-hardening sealant is used to bond the substrates, it may flow and contaminate the liquid crystal during the heating process. Thus, a UV sealant has to be used as a sealant to avoid such a problem.
Referring to FIG. 2C, the lower substrate 1 and the upper substrate 3 are attached to each other. Referring to FIG. 2D, a UV ray is irradiated by using a UV irradiating device 9, to harden the sealant 7 (shown in FIG. 1B), thereby bonding the lower substrate 1 and the upper substrate 3. Then, the bonded substrates 1 and 3 are cut into a unit cell (not shown). A final inspection is carried out.
Thus, the liquid crystal dropping method takes less time period than the vacuum injection method because the liquid crystal 5 is directly dropped onto the lower substrate 1 before the substrates 1 and 3 are bonded.
However, the related art liquid crystal dropping method has the following disadvantages caused by difficulty in determining an accurate amount of the liquid crystal depending upon a size of the substrate and a cell gap between the substrates.
First, if a dropped amount of the liquid crystal is less than the required amount, regions of the substrate for the liquid crystal are filled imperfectly. Particularly, there occur at four corners located farthest from the center of the substrate. These deteriorate uniformity of the cell gap and picture characteristics.
Second, if the liquid crystal is dropped excessively, the liquid crystal comes into contact with the sealant before the sealant is hardened. Thus, the liquid crystal is contaminated.
Third, even if the liquid crystal is dropped appropriately, it takes time to spread the liquid crystal from the center part of the substrate to the corners, the farthest spots. Accordingly, if the imperfectly filled region occurs as the liquid crystal is not spread to the corner-regions, a final inspection cannot be carried out.